Single axle trailer?
You can change the total rpms with the prop diameter without changing the prop, which is why slip is sorted 1st as is pretty well constant between diameter.. thu more cupping , or change the rake will also do so for fine tuning.. and bow high or low.
You can weight the total boat weight on the trailer with a tape measure and set of bathroom scales.. thu you have to be accurate with the distance measurements.
Bit of old high school maths and physics.
Its in several older posts, and have as a note here somewhere.. just got to find it somewhere on the network here ...
Still on my desktop from the last time posted it posting as it is.
"Hmmm single axle trailer
Did you know you can weight the boat (only the boat) on the trailer with bathroom scales?
keep the engine tilt as low was possible, but high enough to just clear the ground..
measure all weights in lbs
measure All distances in inches
1/Put the sales under the hitch, a length timber long enough to JUST lift the hitch and take the weight on the scales... with trailer level or slightly low at the front.
record the weight call it w1
2/ slide the boat back on the trailer about 12" to 20"
measure the distance accruately and record it d1.. the accuracy of this measurement is very critical to the end result
d1
3/ now with hitch same height record the weight as before You may not be able to move the boat a full 20" as the balance on the trailer may put the hitch up in the air....if so just move back till just have enough weight to measure at the hitch....OR put a known weight on the bow deck.. say a 40L water container full right at the start , before taking 1st weight (W1)
OR simply move a lot of stowed gear equipment well forward.
Measure this weight w2
4/ now measure the distance from the center where the bit of wood its on the scales to the center of the axle.
d2
Boat weight = d2(w1-w2)/d1
If put an extra weight on the bow of the boat, now subtract that weight.
Sounds strange.. like stuff like center gravity, weight of trailer etc... If one does the full calculation create the full equation, including these constants and gravity , center of mass and stuff....then compact the equation, all those factors cancel out and one is left with the above equation. Therefore if the constants like trailer weight... which we dont know cancel themselves out then we dont need that information in the 1st place lol
Ok yesterday tested a bungy/ nylon rope painter...
nylon cause it has a strectch and poly doesnt.
Stop the jerk when the boat slides of the keel trailer fast, and comes to a sudden stop at the end of the painter.
Nylon ropes where expensive
Was in Smart Marine other day and in the bin was a packet nylon painter exact length wanted....and a bundle of 6mm bungy, 3x times the length needed... thu at that stage didnt know how many length would be required.
The painter looped on the winch pedestal was about 1.5m beyond the end of the trailer...with it on the bollard, that put the boat about 1m beyond.
I looped the bungy 3 times.. each end and in the middle.. this enabled my to have 1 or 2 or 3 lengths to adjust the 'spring'...and about 1m short of the end of the trailer.
Then worked cable ties in thru the nylon rope and around the bungy cords, not tight and about every 750mm
Testing spring beside the boat in the drive, we could imagine it rolling off then springing back up 1/3 of the way on the trailer...
So attached the painter and bungies to the bollard, and to the winch post, hooked the loops up onto the bow rail.
Tide was still very low, and to get any depth would have meant dropping the trailer wheels over the end of the concrete...which meant the rear center roller was still a good 3" above the water...
Decided to use a double length bungy.
And yeah the boat pushed off the winch stop quite easy.. no need to roll back hit the anchors.
Came to the end of the bungy just over 3/4 down, dropped nive over the last roller, moved out from the trailer about1/2m and came back in against the center roller nice and held there, even thu the side current turns the stern sideway.. which as turned out was good
Un hooked the painter off the winch post, enough stretch to walk around the water , up on the pontoons , flip it over the trailer guide poles and secure the boat at the pontoons.
And still have dry feet.
Note: the nylon painter is only there just in case a bungy loop fails .. to stop the boat floating off into someone elses
And yes realised why ppl dont let the boats down on the winch hook.. or rather, slide off with winch rope on..besides the sudden jerk at the end, stress on winch bushes etc.
We thought it thru just before pushing the boat off...
Its because you have to walk down to the end of the trailer to un hook it.
Its still best to have good winch bushes, lube with none petroleum based oil/ grease, and pull out when parking up.
Now for those who want to join, put a loop in a bungy.
you cant tie a knot, it will undo, and if not undo will slip as the strains diameter shrink under load.
So making a loop..with a good length of tag for a hand hold
and loosely put a cable tie around both where you want the loop to end.
put the loop over a bollard or similar, and pull as much stretch under the area where the cable tie is , and pull up the cable tie tight as... a 2nd person.
Check the loop size.
If a little big repeat with the next tie about 5mm from the 1st...3 ties should do it, I use 4.
Use tie widths slightly less than the diameter of the bungy."
Rem accurate measurements..